Dormouse, hazel (Muscardinus avellanarius)

The hazel dormouse population has declined by a third since 2000 (Photo: MikeLane45/iStock).

Dormice hibernate throughout the winter and spend much of their life asleep. (Photo: WTML)

Dormice feed on berries, which are particularly important before hibernation. (Photo: MikeLane45/iStock)

The loss of woodland is a threat to dormice survival. (Photo: KatPaws/iStock)

Also know as: common dormouse

Scientific name:Muscardinus avellanarius

Family: Gliridae

Appearance

Dormice have golden-brown fur, large eyes and ears and a long furry tail. They have a whole body length of just 10-17cm and weigh no more than 40g.

Where and when to spot

Once found across England and Wales, dormice are now largely restricted to southern England, with a few scattered populations in the Midlands, Wales and Lake District. The species needs diverse woodland and hedgerows to survive, and the loss and degradation of such habitat has driven its decline. Fingle Woods, Devon is a perfect example of the kind of habitat dormice require.

Dormice hibernate through the winter and may spend as much as seven months of the year asleep. In the spring and summer they spend the day sleeping and emerge at night to search for food among tree branches. You would need to be very lucky to see a dormouse in the wild, but may come across their signs. If you find a hazel nut with a smooth circular hole in the shell, the chances are it was made by a feeding dormouse

Feeding

The dormouse diet varies with the time of year. After emerging from hibernation, they feed on flowers, before moving on to insects such as caterpillars in summer. In autumn, dormice prepare for hibernation by eating nuts, seeds and berries, putting on the fat needed to survive the winter.

Behaviour and breeding

Dormice typically give birth to a litter of four to five young each summer. The young are born in a nest woven from grass and small strips of bark and located among tree branches or in a hedge. At first they are pink, furless and blind and their mother puts in a lot of effort looking after them. They stay with her for six to eight weeks, giving them time to develop. By 13 days they are fully furred and have sight at 18 days.

When they are around three weeks old the young start to forage with their mother until they are ready to leave the nest. The young keep their grey fur until they are a year old and sexually mature, then it changes to a ginger-brown colour.

Threats

The loss of ancient woodland and hedgerows across the UK has had a serious impact on dormouse numbers and much of what habitat remains is highly fragmented. Dormice will not leave the safety of the trees to cross large open spaces, meaning populations become increasingly isolated, lose genetic diversity and are more vulnerable to extinction. Traditional forestry methods such as coppicing created favourable habitat for dormice and the abandonment of such methods has also hurt dormice numbers. Additionally, there are concerns that climate change is disrupting the species’ hibernation cycle, meaning dormice awake early when sufficient food is not available.

The dormouse population is thought to have declined by a third since 2000 alone. Conservation methods include managing existing woodland in a dormouse-friendly way and providing nest boxes for the species to use (these can then be monitored to gain an insight into population trends).

Did you know?

If food availability is low or there is bad summer weather, dormice can enter a state known as ‘torpor’ - curling up and sleeping in their nest to save energy and avoid losing weight.

Parts of the UK are also home to the edible dormouse (Glis glis), which was introduced from mainland Europe. This species has grey fur and is around five times larger than a hazel dormouse.